In the art of pressure fluid actuated reciprocating piston percussion rock drills and similar percussion tools, it is known to provide the general configuration of the tool to include a sliding sleeve type valve for distributing pressure fluid to effect reciprocation of a fluid actuated piston hammer. There are many applications of these types of drills wherein the diameter of the hole to be drilled is relatively small, in the range of two to three inches, for example. Still further, there are also applications for reciprocating piston percussion rock drills and similar tools wherein the tool must be inserted within a conduit or tubing string for cleanout of the conduit or for utilization of the conduit as a guide structure.
One improvement in small diameter reciprocating piston percussion rock drills and the like is disclosed and claimed in my U.S. Pat. No. 5,680,904, issued Oct. 28, 1997. The percussion rock drill disclosed in the '904 patent includes opposed sleeve type valves disposed on opposite reduced diameter end portions of the reciprocating piston hammer, respectively, for movement with the piston hammer and for movement relative to the piston hammer to distribute pressure fluid to opposite sides of the piston hammer to effect reciprocation of same. Another advantageous design of a relatively small diameter fluid actuated percussion rock drill is disclosed and claimed in U.S. Pat. No. 4,828,048 to James R. Mayer and William N. Patterson. The drill described and claimed in the '048 patent utilizes a single sleeve type distributing valve disposed at the fluid inlet end of the drill cylinder. However, the construction of a drill in accordance with the '048 patent tends to restrict the minimum outside diameter or require that the fluid passages and/or the piston diameter be of inadequate size for certain applications.
Accordingly, since it is desirable to provide maximum drilling energy in most applications of percussion rock drills within the constraints of the requirements of the outer diameter of the drill, and it is also considered desirable to be able to "steer" the drill in certain applications thereof, there have continued to be needs for improvements in the construction of relatively small diameter hydraulic or other pressure fluid actuated percussion rock drills. It is in pursuit of these objectives that the present invention has been developed.